Version: 2.0.1

It's also a very strange choice to put this tag under forge's namespace instead of aquaculture's.

Thanks for your report!
I can't reproduce the issues with Aquaculture 2.0.1, must be some other mod messing up tags? Or maybe JEI being oudated.
The reason fillet_knife is under Forge's namespace is that it's intended to be working with other mods that tag their stuff the same.

Might be an issue on the pack/server I saw it on then, will answer again if I reproduce it alone when I'll have the time.